This invention concerns an optical interconnection system, particularly applicable to the interconnection of several electronic circuit boards to allow them to communicate between each other.
Information exchange in optical form between electronic boards is attractive due to the transmission speed that increases the throughput, and because it eliminates all constraints on distances between boards and is immune to parasites.
Telecommunications links within a campus area**** are served mainly by dedicated Subscriber Connection Units called hubs, located in technical rooms on the sites to be connected. These hubs interconnect subscribers, mostly at 10 Mbits/sec. at the present time, in clusters of 10 to 100 (1 to 16 boards each handling 8 to 16 or more subscribers). Since access technologies are improving, the binary throughput available in practice is tending to increase (proposals for 25, 50 and 100 Mbits/sec.). The effect of this situation is to incite a need for global exchanges in hub back panels, increasing from 300/500 Mbits/sec. (current situation) to 2/10 Gbits/sec. (1995 situation). Induced exchanges take place between hub boards in a manner which is not very predictable (standard implementation); each board can generate up to 500/1000 Mbits/sec at peak flow, and exchanges may be multicast (several boards receiving at the same time). Current implementations (up to 4 Gbits/sec.) prefer "all electric" solutions on bus 1 to N, each board transmitting alone on part of the bus (statically), while all others are listening. The electrical technology can carry between 20 and 50 Mbits/sec. through each connector point, and problems of back panel characteristic impedance become severe as the throughput increases; in practice it is necessary to connect high density miniature connectors with several hundreds of pins, and a large area of copper for implementation of line drivers/receivers.
Technically, the interconnection need is waiting for a renewal of these solutions in the form of an optical emission architecture in the back panel enabling the interconnection of 16 boards, each capable of sending up to 1 Gbits/sec. to one or several other boards at a given instant.